In a mobile telecommunications network, a user equipment connects to a cell (also known as “camping” or “pairing”) to access the network and use the network service. As the network typically includes a plurality of cells, cell selection is a process of selecting the most appropriate cell for a user equipment to connect to. It is important to optimize the cell selection process in order to improve the quality of the service, both from the point of view of the network service provider and the customer. For example, while operating according to individual operation-level and business-level priorities, network service providers generally aim to maximize the number of satisfied customers at any given point by ensuring that user equipments are connected to the most appropriate cell, thus maximizing the quality of the network service.
A user equipment initially connects to a network by cell selection, but also periodically reconnects to the network (e.g. via the same or another cell) to maintain a quality service. This reconnection process is sometimes referred to as ‘cell reselection’, but is covered by the term ‘cell selection’ at least for the purposes of this description.
The cell selection process involves the user equipment using a cell selection algorithm to connect to a high priority cell. Thus, when the initial cell selection process starts, a cell selection algorithm is performed and the user equipment connects to the highest priority cell.
Subsequently, the user equipment periodically uses the cell selection algorithm to determine a high priority cell (or list of cells), and connects to the high priority cell during reconnection. The user equipment monitors paging and system information from the cell and performs radio measurements and monitoring, and uses this information when performing the cell selection algorithm.
The cell selection process is generally started by the user equipment, but can be influenced by another network node (e.g. the network management system (Base Station Controller)), to encourage or direct the user equipment to connect to a specific cell. This may occur when the network service provider is balancing network load, directing a user equipment to connect to an operator-specific cell, or to avoid “ping-ponging”, for example.
Various cell selection algorithms have been developed for cell selection, such as described in “Cell Selection in 4G Cellular Network”, IEEE International Conference on Computer Communications, 2008, Amzallag, D., et al.; “Cell Search and Cell Selection in UMTS LTE” application note reference 1MA150_0E, 2009, available from http://www2.rohde-schwarz.com/file_12728/1MA150_0E.pdf; “Intelligent Cell Selection Satisfying User Requirements for Inter-System Handover in Heterogeneous Networks”, Computer Communications, 2012, Lee. J. C. & Yoo, S. M.; and “A Proposal of Cell Selection Algorithm for LTE Handover Optimization” in IEEE Symposium on Computers and Communications, 2012, Komine T., Yamamoto, T., & Konishi, S. However, there are problems with these existing cell selection algorithms.
Firstly, these algorithms tend to give a disproportionate preference to cells in close spatial relationship with the user equipment. This can lead to load-balancing issues when a large number of user equipments congregate in a small area (e.g. a city centre), when neighbouring or overlapping cells may have been able to provide an adequate service to the user equipments.
Secondly, some of the cell selection algorithms use quality or experience based approaches, which rely on data between the user equipment and the cell. However, if the user equipment has never connected to the particular cell before, (e.g. it is new to a network, has switched providers, or has ‘roamed’ into the network) then that information will not be available and the cell selection algorithm becomes inaccurate.
Furthermore, such quality or experience based approaches assume that the user equipment's past information remains static and therefore relevant to future cell selections. However, this is not a reliable assumption as most modern user equipments are customizable and upgradable, and cell parameters are reconfigurable and often adaptive.
Thirdly, some cell selection algorithms are based on instantaneous data alone (rather than using past quality information). However, this can be inappropriate as the instantaneous information may not be accurate when considered over a longer period of time. Thus, a user equipment may select a cell based on the data applicable during the cell selection process, but that cell may quickly become unsuitable and the user equipment remains camped on the cell until cell reselection.
Fourthly, some alternative cell selection algorithms require modification of the user equipment, the parameters broadcast by the cell basestations, or the parameters of the signalling protocols between cells and the user equipments. However, this is unlikely to be appropriate in strictly standardized mobile telecommunications environments, particular when the radio operations of the user equipment is based on regulated commodity hardware.
It is therefore desirable to alleviate some or all of the above problems.